Project Abstract Coronary microvascular dysfunction (CMD) due to changes in the function and structure of coronary microcirculation in the absence of obstructive coronary artery disease (CAD) is poorly understood, and ischemia with no obstructive CAD (INOCA) and myocardial infarction with no obstructive CAD (MINOCA) are increasingly observed in women and men. More than two decades of work has led us to conclude that CMD can lead to heart failure with preserved ejection fraction (HFpEF). Our findings indicate that risk factor conditions (hypertension, obesity, dyslipidemia, dysglycemia, estrogen loss) promote a pro-inflammatory, pro-oxidative state, rendering the coronary microvasculature and myocardium vulnerable to: 1) ischemia, 2) micro-infarction-related myocardial scar, 3) diffuse fibrosis, 4) adverse LV remodeling. We propose that CMD plays a critical role in a ?pre-HFpEF state?.Despite delineation of HFpEF into specific phenotypes, no effective treatments exist. The current application will address this therapeutic knowledge gap by investigating CMD-related ischemia as a precursor of myocellular damage, scar, diffuse fibrosis, and LV diastolic dysfunction (hallmark features of HFpEF). Indeed, CMD is associated with measurable increases in high sensitivity cardiac troponin (hs-cTnI), and hs-cTnI elevations predict future HFpEF. Once established, we will be well positioned to aggressively target identified mechanistic targets in a specific well-characterized at-risk population, with the primary goal of preventing progression to HFpEF. Our application directly addresses the NHBLI Strategic Vision 4.CQ.05 ?How does the pathobiology that underlies nonobstructive ischemic heart disease and the associated risks for acute coronary syndrome and early mortality differ between subpopulations, and what are the targets for treatment and prevention?? We propose the following to address this: Aim 1: Test the hypothesis that CMD-related ischemia contributes to myocellular damage and impaired ventricular relaxation. CMD will be measured directly, using our established intracoronary pharmacological vasoactive protocol, in subjects with signs/symptoms of ischemia but no obstructive CAD perform provocative stress testing while myocardial ischemia will be assessed directly through invasive simultaneous arterial and coronary sinus/great cardiac vein oxygen tension and lactate measurements, and continuous ECG?s recordings, while left ventricular function will be directly assessed using Millar-catheter LV pressure-volume loops and stress-induced myocellular damage will be directly measured by coronary sinus/great cardiac vein hs-cTnI. Aim 2: Test the hypothesis that CMD-related ischemic myocellular damage contributes to LV diastolic dysfunction progression. Subjects from Aim 1 will also undergo comprehensive cardiac magnetic resonance imaging (CMRI) at enrollment and 1-2 years later. We will evaluate CMRI LV perfusion, myocardial scar, diffuse fibrosis, LV remodeling, and diastolic function. We will leverage the strengths and resources of our world-renowned proteomics core to establish evidence of chronic myocellular damage using prospectively repeated ambulatory hs-cTnI determinations. Combining the results of our ongoing WARRIOR trial (NCT#03417388) results with the current application will identify potential mechanistic treatment targets of: 1) ischemia/scar, 2) strain/remodeling, and 3) fibrosis/ventricular stiffness, for mechanistically supported HFpEF prevention clinical trials such as: 1) anti-ischemic/scar therapies (statin/ACE-ARB, alpha-beta blockers, NO-cyclic GMP), 2) strain/remodeling therapies (sacubitril/valsartan), and/or 3) anti-fibrotic therapies (galectin 3, peptidyl arginine deiminase type IV inhibitor, stress-activated kinase-1 inhibitor, protein kinase G, fibroblast growth factor).